ABB RELION 650 SERIES, Technical Manual

Page: 180 / 942

The polarizing voltage is available as long as the positive-sequence voltage
exceeds 5% of the set base voltage
UBase . So the directional element can be used
for all unsymmetrical faults including close-in faults.
For close-in three-phase faults, the U1
L1M
memory voltage, based on the same
positive sequence voltage, ensures correct directional discrimination.
The memory voltage is used for 100 ms or until the positive sequence voltage is
restored.
After 100 ms, the following occurs:
• If the current is still above the set value of the minimum operating current (7%
of the set terminal rated current
IBase ), the condition seals in.
• If the fault has caused tripping, the trip endures.
• If the fault was detected in the reverse direction, the measuring element
in the reverse direction remains in operation.
• If the current decreases below the minimum operating value, the memory
resets until the positive sequence voltage exceeds 10% of its rated value.
The directional setting is given as a characteristic angle AngleRCA for the function
and an angle window ROADir .
U
ref
I
dir
RCA
ROA
Forward
Reverse
ROA
en05000745.vsd
IEC05000745 V1 EN-US
Figure 83: Directional characteristic of the phase overcurrent protection
Section 7
1MRK 506 382-UEN A
Current protection
174 Line distance protection REL650 2.2 IEC
Technical manual